Tachometers have been used for many years to provide a rate signal in servo control systems or to provide rate damping for system stabilization. In servo systems operating at low speeds the tachometers are normally of the DC brush type which provide an analog voltage having an amplitude proportional to speed. However, brush type tachometers do not perform well at high speeds due to brush bounce and brush wear problems. Digital type tachometers, on the other hand, operate well at high speeds in the range where the digital pulse rate has sufficient band width. The digital tachometers, however, do not perform well at low speeds, particularly at speeds close to zero where the interval between pulses is too great.
An object of this invention is to provide a DC tachometer operable over a wide speed range from substantially zero to high speeds.
Another object is to provide a brushless DC tachometer providing an output voltage proportional to speed over a wide range with relatively little ripple content in the output signal.